1. Field of the Invention
The present invention relates to a production method and a production apparatus of a ceramic green sheet. More specifically, it relates to a method and an apparatus for producing a ceramic green sheet with a carrier film lined thereon.
2. Description of the Related Art
In producing a laminated ceramic electronic part such as a laminated ceramic capacitor, ceramic green sheets are laminated. In order to achieve a high performance as well as a smaller size or a thinner shape of the laminated ceramic electronic part, it is effective to have the ceramic green sheets as a thin layer.
On the other hand, a ceramic green sheet is mechanically weak. Therefore, in the case of the above-mentioned thin layer, a flexible carrier film is prepared to be applied with a ceramic slurry for forming a ceramic green sheet in order to compensate the mechanical strength. The method uses a doctor blade to apply the ceramic slurry, and hence, may be referred to as the doctor blade method. And further, the ceramic green sheet is handled in a state lined with the carrier film in the subsequent steps.
As mentioned above, a doctor blade method has been used conventionally for forming a ceramic green sheet on a carrier film.
However, the above-mentioned doctor blade method involves a problem in that a comparatively large irregularity tends to generate in terms of the thickness of the obtained ceramic green sheets because the thickness of the obtained ceramic green sheets fluctuates according to the physical property of the ceramic slurry, such as the viscosity, the specific gravity, and the solid component concentration, and according to the liquid level change in the tank for storing the ceramic slurry to be supplied to the doctor blade part by the ceramic slurry consumption.
On the other hand, as a method for forming a coat film such as an adhesive on a carrier film, a method of using a slurry coater comprising a slurry room provided with an opening toward the outside for receiving a coating liquid (slurry) supply with a doctor edge formed along one side rim of the opening has been considered. According to the method, a coat film of a slurry can be formed on a carrier film by supplying the slurry to the slurry room and pressing the carrier film to the fringe part of the opening of the slurry room so as to close the opening, and moving the carrier film along the opening such that the doctor edge exists at the downstream side.
In this method, since the internal pressure of the slurry room is one factor to influence the coat film thickness to be formed on the carrier film, it is important to constantly maintain the pressure in the slurry room for evening the coat film thickness.
Therefore, a method of constantly maintaining the pressure in the slurry room by providing a pressure sensor in the slurry room for always measuring the pressure in the slurry room so that the pressure on the slurry to be sent into the slurry room can be controlled based on the measurement result can be considered.
However, if the pressure of the slurry to be sent is controlled based on the measurement result by the pressure sensor as mentioned above, since the pressure sensor is provided inside the slurry room, the pressure sensor tends to function too sensitively so that the pressure of the slurry to be supplied to the slurry room is frequently changed, resulting in an inconvenience that the coat film thickness fluctuates therefor.
Accordingly, if this method of using a slurry coater is to be adopted as a method for forming a ceramic green sheet on a carrier film, it is disadvantageous in that the film thickness irregularity of the green sheets is large so that a laminated ceramic electronic part cannot be obtained with stable characteristics. The smaller the electronic part is, the larger the disadvantage is.